In general, electric vehicles (EV) and hybrid vehicles (HV) have structures with low sound emission and are superior in quietness to gasoline-powered vehicles. In contrast, an engine sound emitted from such a gasoline-powered vehicle is one element from which a pedestrian notices approach of a vehicle or a driver receives a speed feeling or a travelling feeling; thus, it is impossible to unconditionally deny such a sound. There has been proposed a technique for EVs or HVs to emit a fake engine sound to a cabin of a vehicle or to the outside of the vehicle (for example, PTLs 1, 2). The fake engine sound is an electronically-processed sound that evokes an engine sound of a vehicle or a travel sound including an engine sound.
PTL 1 discloses a technique of controlling a sound volume of the fake engine sound based on a driving environment of a vehicle. For example, the disclosure includes a technique of reducing the sound volume of the fake engine sound or muting the fake engine sound to make ambient sounds easily caught while a vehicle is travelling along a route guided by a car navigation, at a railroad crossing, or near an urban area. The disclosure further includes a technique of increasing the sound volume of the fake engine sound to alert a driver when, for example, a vehicle speed exceeds a speed limit.
Further, PTL 2 discloses a technique of controlling a volume of a fake engine sound based on a vehicle cabin environment. The disclosure includes, for example, a technique of increasing the sound volume of the fake engine sound during playback of a rock-style music, and reduces the sound volume of the fake engine sound during playback of a classic-type music or a conversation made by an occupant.